The present invention relates in general to output level indicating and more particularly concerns novel apparatus and techniques for indicating the range embracing the instantaneous amplitude of an output signal level with reliable techniques that avoid delays inherent in mechanical indicating systems. Yet the apparatus is relatively inexpensive and reliable.
It is customary to use output VU meters to indicate the output signal level of an audio amplifier or tape recorder. A purpose of such indicators is to enable the user to adjust the amplification so as to avoid overload. That is to say, it is often desirable to set the amplification as high as possible consistent with avoiding overload upon occurrence of expected peak amplitudes. Thus, signals having the maximum expected peak amplitude are applied to the input and the amplifier gain adjusted so that the instantaneous maximum deflection of the meter does not exceed a predetermined value, such as zero dB on the meter scale. The difficulty with this approach is that the inertia of the meter movement is too great to respond to peak amplitudes that occur for a very short duration.
For further background reference is made to 51 Journal of the Acoustical Society of America 1777-80 (1972) published after the circuit of FIG. 2 was built, tested and found to work satisfactorily in achieving the objects set forth below.
Accordingly, it is an important object of this invention to provide methods and means for indicating the peak amplitude of an amplifier output signal.
It is another object of the invention to achieve the preceding object with an instantaneous peak that occurs for very short duration.
It is still a further object of the invention to achieve one or more of the preceding objects while providing a positive indication for amplifier overload.
It is a further object of the invention to achieve one or more of the preceding objects with a display of pleasing appearance.
It is a further object of the invention to achieve one or more of the preceding objects with apparatus that displays peak amplitudes in meaningful increments in a clear and unambiguous manner with reliable inexpensive apparatus.